Mercaptoalkanoylamino lactams have been disclosed as possessing useful cardiovascular properties as a result of their activity as dual angiotensin converting enzyme inhibitors and neutral metalloendopeptidase inhibitors. The lactam can be a moncyclic, fused bicyclic or fused tricyclic as taught by Karanewsky et al. in U.S. Pat. No. 5,552,397, Karanewsky in U.S. Pat. No. 5,504,080, Robl in U.S. Pat. No. 5,508,272, Robl in U.S. Pat. No. 5,525,723, Robl in U.S. Pat. No. 5,362,727, Robl in U.S. Pat. No. 5,587,375, Robl et al. in U.S. Ser. No. 443,278 filed May 17, 1995, now U.S. Pat. No. 5,877,313, and EP 744,319, Ryono et al. in U.S. Pat. NO. 5,635,504 and Karanewsky et al. in U.S. Pat. No. 5,650,408.
These references disclose coupling an acylmercaptoalkanoic acid sidechain to the amino lactam ester followed by deprotection by treatment with sodium hydroxide or lithium hydroxide in aqueous alcohol or tetrahydrofuran followed by treatment with aqueous acid to give the desired mercaptoalkanoylamino lactam products.
This invention is directed to an improvement in the deprotection processes used to convert an acylmercaptoalkanoylamino lactam acid or ester of the formula 
to the mercaptoalkanoylamino lactam acid or ester of the formula 
and an improvement in the deprotection process used to convert the mercaptoalkanoylamino lactam ester of formula I to the mercaptoalkanoylamino lactam acid of formula I.
These deprotection reactions are performed under basic conditions. The mercapto group in the lactam acid or ester of formula I under such conditions is susceptible to the formation of disulfides of the formula 
Such disulfides are themselves an unwanted impurity in the pharmaceutically active mercaptoalkanoylamino lactam acid products of formula I. Also, the disulfides of formula III can convert to other undesirable side-products. In particular, when R1 is other than hydrogen, the disulfide of formula III can convert to the mercaptoalkanoyl lactam of formula I having the undesired chirality at the optically active carbon in the mercaptoalkanoyl sidechain.
Similarly, the formation of the disulfide impurity of formula III can occur during recrystallization of the mercaptoalkanoylamino lactam product of formula I.
The improvements of this invention reside in including within the above deprotection and recrystallization processes an agent that minimizes the amount of the disulfides of formula III and, in turn, minimizes the formation of the undesired epimer of the pharmaceutically active compound of formula I.
Preferred agents for this purpose are bismercaptans as well as reducing agents such as phosphines and phosphites, zinc metal powder, and sodium hydrosulfite.
The amino lactam acids and esters X1 shown above include: 
In the above formulas, the various symbols have the definitions listed below.
R1 and R2 are independently selected from straight or branched chain alkyl of 1 to 6 carbons, xe2x80x94(CH2)m-aryl, xe2x80x94(CH2)m-substituted aryl, or xe2x80x94(CH2)m-heteroaryl.
m is zero or an integer from 1 to 6.
n is zero or one.
R4 and R5 are independently selected from hydrogen, alkyl, substituted alkyl, alkenyl, xe2x80x94(CH2)m-cycloalkyl, xe2x80x94(CH2)m-aryl, xe2x80x94(CH2)m-substituted aryl, or xe2x80x94(CH2)m-heteroaryl, or one of R4 and R5 is hydrogen and the other is hydroxy, or R4 and R5 taken together with the carbon to which they are attached complete a saturated cycloalkyl ring of 3 to 7 carbons, or R4 and R5 taken together with the carbon to which they are attached complete a keto substituent.
R6, R8 and R10 are independently selected from hydrogen, alkyl, substituted alkyl, alkenyl, xe2x80x94(CH2)m-cycloalkyl, xe2x80x94(CH2)m-aryl, xe2x80x94(CH2)m-substituted aryl, or xe2x80x94(CH2)m-heteroaryl.
R7, R9 and R11 are independently selected from hydrogen, alkyl, substituted alkyl, alkenyl, xe2x80x94(CH2)m-cycloalkyl, xe2x80x94(CH2)m-aryl, xe2x80x94(CH2)m-subsituted aryl, or xe2x80x94(CH2)m-heteroaryl or R6 and R7 taken together with the carbon to which they are attached complete a saturated cycloalkyl ring of 3 to 7 carbons, or R8 and R9 taken together with the carbon to which they are attached complete a saturated cycloalkyl ring of 3 to 7 carbons.
b is zero or one.
d is zero or one.
q is an integer from 1 to 4.
r is one or two.
t is an integer from 1 to 3.
v is one or two.
w is one or two.
Y1 is xe2x80x94CH2xe2x80x94, xe2x80x94(CH2)2xe2x80x94, xe2x80x94(CH2)3xe2x80x94, xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, xe2x80x94CH2xe2x80x94Oxe2x80x94, or xe2x80x94CH2xe2x80x94Sxe2x80x94.
Y2 is xe2x80x94CH2xe2x80x94 xe2x80x94Sxe2x80x94, or xe2x80x94Oxe2x80x94.
Y3 is xe2x80x94CH2xe2x80x94, xe2x80x94(CH2)2, xe2x80x94(CH2)3xe2x80x94, xe2x80x94Oxe2x80x94 or xe2x80x94CH2xe2x80x94Oxe2x80x94.
Z is O or two hydrogens.
R17 is hydrogen, alkyl, substituted alkyl, alkenyl, xe2x80x94(CH2)m-cycloalkyl, xe2x80x94(CH2)m-aryl, xe2x80x94(CH2)m-substituted aryl, or xe2x80x94(CH2)m-heteroaryl.
Y5 is xe2x80x94CH2xe2x80x94, xe2x80x94Sxe2x80x94, or xe2x80x94Oxe2x80x94 provided that Y5 is xe2x80x94Sxe2x80x94 or xe2x80x94Oxe2x80x94 only when d is one.
Y6 is xe2x80x94Sxe2x80x94 or xe2x80x94Oxe2x80x94.
the dashed line --- represents an optional double bond between the two carbons. 
represents an aromatic heteroatom containing ring selected from 
Y7 is xe2x80x94Sxe2x80x94 or xe2x80x94NHxe2x80x94.
Y8 is xe2x80x94Sxe2x80x94, xe2x80x94Oxe2x80x94 or xe2x80x94NHxe2x80x94.
R18 and R19 are independently selected from hydrogen, alkyl, xe2x80x94(CH2)m-aryl, or R18 and R19 together with the carbon and nitrogen atoms to which they are attached complete a five or six membered ring.
R12 is hydrogen or an acid protecting group such as methyl, ethyl, propyl, phenyl or benzyl.
The term xe2x80x9calkylxe2x80x9d refers to straight or branched radicals of 1 to 7 carbons, preferably 1 to 4 carbons.
The term xe2x80x9csubstituted alkylxe2x80x9d refers to such straight or branched chain radicals of 1 to 7 carbons wherein one, two or three hydrogens have been replaced by a hydroxy, amino, cyano, Cl, Br, F, trifluoromethyl, xe2x80x94NH(alkyl of 1 to 4 carbons), xe2x80x94N(alkyl of 1 to 4 carbons)2, alkoxy of 1 to 4 carbons, alkylthio of 1 to 4 carbons, or carboxy. The preferred xe2x80x9csubstituted alkylxe2x80x9d is of 1 to 4 carbons with one hydrogen replaced by hydroxy, amino, Cl, or Br.
The term xe2x80x9calkenylxe2x80x9d refers to straight or branched chain radicals of 3 to 7 carbon atoms having one or two double bonds. Preferred xe2x80x9calkenylxe2x80x9d groups are straight chain radicals of 3 to 5 carbons having one double bond.
The term xe2x80x9ccycloalkylxe2x80x9d refers to saturated rings of 3 to 7 carbons with cyclopropyl, cyclobutyl, cyclopentyl, and cyclohexyl being preferred.
The term xe2x80x9carylxe2x80x9d refers to phenyl, 1-naphthyl and 2-naphthyl with phenyl being preferred.
The term xe2x80x9csubstituted arylxe2x80x9d refers to phenyl, 1-naphthyl and 2-naphthyl having a substituent selected from alkyl of 1 to 4 carbons, alkoxy of 1 to 4 carbons, alkylthio of 1 to 4 carbons, Cl, Dr, F, hydroxy, trifluoromethyl, amino, xe2x80x94NH(alkyl of 1 to 4 carbons), or xe2x80x94N(alkyl of 1 to 4 carbons)2, di and tri-substituted phenyl, 1-naphthyl, or 2-naphthyl wherein said substituents are selected from methyl, methoxy, Cl, Br, methylthio, hydroxy or amino.
The term xe2x80x9cheteroarylxe2x80x9d refers to unsaturated rings of 5 or 6 atoms containing one or two C and S atoms and/or one to four N atoms provided that the total number of hetero atoms in the ring is 4 or less. The heteroaryl ring is attached by way of an available carbon or nitrogen atom. Preferred heteroaryl groups include 2-, 3-, or 4-pyridyl, 4-imidazolyl, 4-thiazolyl, 2- and 3-thienyl and 2- and 3-furyl. The term heteroaryl also includes bicyclic rings wherein the five or six membered ring containing O, S and N atoms as defined above is fused to a benzene or pyridyl ring. Preferred bicyclic rings are 2- and 3-indolyl and 4- and 5-quinolinyl.
The acylmercaptoamino lactam esters of formula II are prepared by coupling the acylmercapto containing sidechain of the formula 
with the amino lactam ester
Hxe2x80x94X1xe2x80x83xe2x80x83(XXV)
The above reaction can be performed in an organic solvent such as methylene chloride and in the presence of a coupling reagent such as 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide, dicyclohexylcarbodiimide, benzotriazol-1-yloxytris-(dimethylamino)phosphonium hexafluorophosphate, or carbonyldiimidazole. Alternatively, the acylmercapto carboxylic acid of formula XXIV can be converted to an activated form such as an acid chloride, mixed anhydride, symmetrical anhydride, activated ester, etc., prior to coupling.
The starting materials of formulas XXIV and XXV and the resulting acylmercaptoalkanoylamino lactam esters of formula II are described in the prior art. For example, the above compounds wherein X1 is as defined in formulas IV to XIV are described by Karanewsky et al. in U.S. Pat. No. 5,552,397 whose disclosure is hereby incorporated by reference. The above compounds wherein X1 is as defined in formula XV are described by Robl in U.S. Pat. No. 5,508,272 whose disclosure is hereby incorporated by reference. The above compounds wherein X1 is as defined in formula XVI are described by Karanewsky in U.S. Pat. No. 5,504,080 whose disclosure is hereby incorporated by reference. The above compounds wherein X1 is as defined in formula XVII are described by Robl in U.S. Pat. No. 5,525,723 whose disclosure is hereby incorporated by reference. The above compounds wherein X1 is as defined in formula XVIII are described by Robl in U.S. Pat. No. 5,362,727 whose disclosure is hereby incorporated by reference. The above compounds wherein X1 is as defined in formula XIX and XX are described by Robl in U.S. Pat. No. 5,587,375 whose disclosure is hereby incorporated by reference. The above compounds wherein X1 is as defined in formula XXI are described by Ryono et al. in U.S. Pat. No. 5,635,504 whose disclosure is hereby incorporated by reference. The above compounds wherein X1 is as defined in formula XXII are described by Karanewsky et al. in U.S. Pat. No. 5,650,408 whose disclosure is hereby incorporated by reference. The above compounds wherein X1 is as defined in formula XXIII are described by Robl et al. in EP 743,319 and in U.S. Ser. No. 443,278 filed May 17, 1995 now U.S. Pat. No. 5,877,313 whose disclosure is hereby incorporated by reference.
The deprotection processes of this invention include conversion of the acylmercaptoalkanoylamino lactam acid or ester of formula II to the mercaptoalkanoylamino lactam of formula I The improvement in this process resides in including in the basic hydrolysis reaction that removes the acyl functional group R2xe2x80x94C(O)xe2x80x94 an agent that minimizes the amount of the disulfides of formula III and, in turn, minimizes the formation of the undesired epimer of the pharmaceutically active compound of formula I.
When the acylmercaptoalkanoylamino lactam of formula II is a carboxylic acid, i.e. R12 in the definition of X1 in formula II is hydrogen, then the acyl protecting group R2xe2x80x94C(O)xe2x80x94 is removed in a single step to give the pharmaceutically active lactam of formula I. This deprotection process involves treating the lactam carboxylic acid of formula II with an alkali metal or alkaline earth metal hydroxide or carbonate or with an amine in a suitable solvent containing a sufficient amount of an agent that minimizes the amount of the disulfides of formula III. Suitable agents for this purpose include bismercaptans as well as phosphine and phosphite reducing agents, zinc metal powder, and sodium hydrosulfite. Such agents can be present in an amount from about 1 mole to about 20 mole percent, preferably from about 5 mole percent to about 10 mole percent in the reaction mixture. This deprotection reaction can be performed at a temperature of from about xe2x88x9220xc2x0 C. to about 45xc2x0 C. Following completion, the reaction is acidified with an aqueous acid such as HCl acetic acid, propanoic acid, sulfuric acid, phosphoric acid, or oxalic acid to precipitate out the pharmaceutically active lactam of formula I.
Suitable alkali metal and alkaline earth metal hydroxides and carbonates for this deprotection process include sodium hydroxide, potassium hydroxide, lithium hydroxide, sodium carbonate, potassium carbonate, and lithium carbonate. Amines useful in this deprotection process include H2N-alkyl, H2Nxe2x80x94(CH2)m-aryl, and hydroxyalkylamines wherein alkyl, aryl, and m are as defined above. Methylamine, ethylamine, benzylamine, and ethanolamine are preferred. Suitable solvents for this deprotection process include methanol, aqueous methanol, ethanol, aqueous ethanol, tetrahydrofuran, aqueous tetrahydrofuran, isopropanol, aqueous isopropanol, acetonitrile, aqueous acetonitrile and water.
When the acylmercaptoalkanoylamino lactam of formula II is a carboxylic acid ester, i.e. R12 in the definition of X1 in formula II is an acid protecting group such as methyl, ethyl, propyl, phenyl or benzyl, then the acyl protecting group R2xe2x80x94C(O)xe2x80x94 and the carboxylic acid protecting group can be removed in a single step or in two steps to give the pharmaceutically active lactam of formula I. In the single step deprotection process, the lactam carboxylic acid ester of formula II is treated under aqueous conditions with an alkali metal or alkaline earth metal hydroxide or carbonate in a suitable solvent containing a sufficient amount of an agent that minimizes the amount of the disulfides of formula III. Suitable agents for this purpose include bismercaptans as well as phosphine and phosphite reducing agents, zinc metal powder, and sodium hydrosulfite. Such agents can be present in an amount from about 1 mole percent to about 20 mole percent, preferably from about 5 mole percent to about 10 mole percent in the reaction mixture. This deprotection reaction can be performed at a temperature of from about xe2x88x9220xc2x0 to about 45xc2x0 C. Following completion, the reaction is acidified with an aqueous acid such as HCl, acetic acid, propanoic acid, sulfuric acid, phosphoric acid, or oxalic acid to precipitate out the pharmaceutically active lactam of formula I.
Suitable alkali metal and alkaline earth metal hydroxides and carbonates for this one step deprotection process are as defined above. Suitable solvents for this one step deprotection process include methanol, ethanol, isopropanol, acetonitrile, and tetrahydrofuran. This reaction is performed under aqueous conditions meaning that water is present in the solvent and/or in the reagents.
The improved deprotection processes of this invention also include the process in which the acylmercaptoalkanoylamino lactam ester of formula II is converted to the mercaptoalkanoylamino lactam ester of formula I. This process involves removal of the acyl group R2xe2x80x94C(O)xe2x80x94 by treating the acylmercaptoalkanoylamino lactam ester of formula II with an alkali metal or alkaline earth hydroxide or carbonate or with an amine in a suitable solvent containing a sufficient amount of an agent that minimizes the amount of the disulfides of formula III and, in turn, minimizes the formation of the undesired epimer of the pharmaceutically active compound of formula I. Suitable agents for this purpose include bismercaptans as well as phosphine and phosphite reducing agents, zinc metal powder, and sodium hydrosulfite. Such agents can be present in an amount from about 1 mole percent to about 20 mole percent, preferably from about 5 mole percent to about 10 mole percent in the reaction mixture. When an alkali metal or alkaline earth metal hydroxide or carbonate is employed, the reaction is performed under non-aqueous conditions. When an amine is employed, the reaction is performed under aqueous conditions. This deprotection reaction is performed at a temperature of from about xe2x88x9220xc2x0 C. to about 45xc2x0 C. Following completion, the reaction is acidified with an aqueous acid such as HCl, acetic acid, propanoic acid, sulfuric acid, phosphoric acid or oxalic acid to precipitate out the mercaptoalkanoylamino lactam ester of formula I.
Suitable alkali metal and alkaline earth metal hydroxides and carbonates and amines for this first deprotection step are as defined above. Suitable solvents include methanol, ethanol, isopropanol, acetonitrile, and tetrahydrofuran.
The improved deprotection processes of this invention also include the process in which the mercaptoalkanoylamino lactam ester of formula I is converted to the pharmaceutically active mercaptoalkanoylamino lactam of formula I wherein R12 is hydrogen. This process involves removal of the carboxylic acid protecting group by treating the lactam ester of formula I with an alkali metal or alkaline earth metal hydroxide or carbonate under aqueous conditions in a suitable solvent containing a sufficient amount of an agent that minimizes the amount of the disulfide of formula III, and in turn, minimizes the formation of the undesired epimer of the pharmaceutically active compound of formula I. Suitable agents for this purpose include bismercaptans as well as phosphine and phosphite reducing agents, and zinc metal powder. Such agents can be present at from about 1 mole percent to about 20 mole percent, preferably from about 5 mole percent to about 10 mole percent in the reaction mixture. This deprotection is performed at a temperature of from about xe2x88x9220xc2x0 C. to about 45xc2x0 C. Following completion, the reaction is acidified with an aqueous acid such as HCl, acetic acid, propanoic acid, sulfuric acid, phosphoric acid, or oxalic acid to precipitate out the pharmaceutically active lactam of formula I.
Suitable alkali metal and alkaline earth metal hydroxides and carbonates for this deprotection step are as defined above. Suitable solvents include water, methanol, ethanol, isopropanol, acetonitrile and tetrahydrofuran.
In the improved recrystallization and reprocessing process of this invention, the mercaptoalkanoylamino lactam product of formula I is added to a suitable solvent containing a sufficient amount of an agent that minimizes the amount of the disulfides of formula III, and in turn, minimizes the formation of the undesired epimer of the pharmaceutically active compound of formula I. Suitable agents for this purpose include bismercaptans as well as phosphine and phosphite reducing agents, zinc metal powder, and sodium hydrosulfite. Such agents can be present at from about 1 mole percent to about 20 mole percent, preferably from about 5 mole percent to about 10 mole percent in the recrystallization mixture. The resulting slurry is subjected to changes in temperature and/or pH, optionally filtered, and then subjected to additional changes in temperature and/or pH to effect the recrystallization. For example, the slurry can be heated at from about 25xc2x0 C. to the reflux temperature to dissolve the solids, the solution is then filtered, the combined filtrates are cooled to about room temperature, and desired product is collected. Alternatively, the slurry is treated to raise the pH above at least about 8 by the addition of a basic material such as an alkali metal or alkaline earth metal hydroxide or carbonate, afterward the pH is lowered to at least below about 8 and preferably below about 6.0 and the product is precipitated out by the addition of an acid such as HCl, acetic acid, propanoic acid, sulfuric acid, phosphoric acid, or oxalic acid, the product is filtered off, washed with water and tert-butyl methyl ether, and dried in vacuo.
Suitable solvents for the recrystallization process include methanol, ethanol, isopropanol and mixtures thereof.
The bismercaptans employed in the above deprotection and recrystallization procedure are compounds which in the presence of the disulfide of formula III will cleave such disulfides by forming a stable ring. Suitable bismercaptans are those of the formula 
wherein k is an integer from 1 to 4 and each X2 is independently selected from hydrogen and hydroxy as well as 1,2-benzenedimethanethiol, 1,3-butanedithiol meso-xcex1,xcex1xe2x80x2-dimercaptoadipic acid, disodium salt, and durene-xcex1(1), xcex1(2)-dithiol. Preferred bismercaptans are dithiothreitol and dithioerythritol. Suitable phosphine reducing agents include tributyl phosphine and triphenyl phosphine. Suitable phosphite reducing agents include triethyl phosphite. The preferred reagent for use in the deprotection and recrystallization reactions of this invention is dithiothreitol.
By minimizing the amount of the disulfides of formula III in the reaction mixture according to the improved deprotection and recrystallization processes of this invention, the by-products of the disulfide of formula III are also minimized. Such by-products include, when R1 is other than hydrogen, the mercaptoalkanylamino lactams of formula I having the undesired chirality at the optically active carbon in the sidechain.
In the preferred embodiments of this invention, X1 in the acylmercaptoalkanoylamino lactam acid or ester of formula II is of formula IV or formula XV, n is zero, R1 is benzyl, and R2 is methyl. When X1 is of formula IV, q is preferably two, R4, R5, R10, and R11 are preferably hydrogen, b is preferably zero, R12 is preferably hydrogen or ethyl, and R6 and R7 are preferably independently selected from hydrogen and alkyl of 1 to 4 carbons, especially where R6 and R7 are both methyl. When X1 is of formula XV, v is preferably two, d is preferably one, Y5 is preferably xe2x80x94CH2xe2x80x94, Y6 is preferably xe2x80x94Sxe2x80x94, and R12 is preferably hydrogen or methyl.
The asterick (*) in formulas I, II and XXIV represent an asymmetric carbon in the acylmercaptoalkanoyl and mercaptoalkanoyl sidechain. In the preferred compounds, this asymmetric center has the absolute configuration S. As shown in formula IV to XXXIII other asymmetric centers are present in the various amino lactam rings.
The pharmaceutically active products of formula I wherein R12 is hydrogen are useful cardiovascular agents particularly useful in the treatment of hypertension and congestive heart failure. The pharmaceutically active products can be formulated in amounts effective for treating hypertension or congestive heart failure as described by Karanewsky et al. in U.S. Pat. No. 5,552,397, Karanewsky in U.S. Pat. Nos. 5,504,080 and 5,650,408, Robl in U.S. Pat. Nos. 5,508,272, 5,525,723, 5,587,375 and 5,362,727, Robl in U.S. Ser. No. 443,278 filed May 17, 1995 and EP 743,319 and, Ryono et al. in U.S. Pat. No. 5,635,504.
The following examples are illustrative of the invention.